Incredible Video Shows Scientists Coming Across Two Underwater Cities Built by Octopuses

An octopus has more limbs than humans can fathom, each of which contains its own brain. With zillions of neurons tingling in its body, this surreal aquatic beast crawls on the sea grass, like a fancy mystery of the deep dark waters. With its trailing tentacles, an octopus can camouflage itself against predators like sharks and sea lions. However, this blue-blooded creature is not always solitary, especially the “Gloomy Octopus.” Unlike what its name might suggest, a gloomy octopus (Octopus tetricus) is not a loner. These octopuses, in fact, have built their own cities in Australia, as scientists revealed in a paper published in Marine and Freshwater Behaviour and Physiology.

Typically, a gloomy octopus is known for its distinctive white eyes and rust-colored arms, with body color ranging from mottled brown to white buttermilk. This eight-legged beast resides mostly in rocky reefs, seagrass beds, and intertidal rocky shores, often squeezing their bodies in narrow fissures to hunt. Previous studies found that these marine mollusks like to remain in solitude. However, this new study has revealed that this might not always be the case. Like sardines and dolphins, they too like to live, feed, and mate alongside their eight-legged fellows and mates. 

This study comes as a story straight out of the 1978 movie Warlords of Atlantis, where a giant octopus named The Sentinel guards the entrance to the lost city of Atlantis and attacks a ship of its size to prevent humans from breaking into the city. It was first in 2009 when scientists discovered that a consortium of gloomy octopuses were living close to each other at a site in Jervis Bay, Australia. The underwater city was dubbed “Octlantis.” Since this city was built around a scrap of metal or a human-made object, the scientists thought that it was just an anomaly. But when they analyzed more octopuses a few years later, it busted this interpretation.

This time too, they found another colony of wild octopuses clustered together on a patch of the rocky outcrop in an area matted with silt. This city consisted of 10 to 15 animals of varying sizes, who were engaged in complex interactions with each other including fighting, mating, chasing, and even evicting, according to BBC Earth. “In addition to the rock outcroppings, octopuses who had been inhabiting the area had built up piles of shells left over from creatures they ate, most notably clams and scallops. These shell piles, or middens, were further sculpted to create dens, making these octopuses true environmental engineers,” explained Stephanie Chancellor, study co-author, in a press release.

"Some of the octopuses were seen evicting other animals from their dens,” added Chancellor. “There were some apparent threat displays where an animal would stretch itself out lengthwise in an 'upright' posture and its mantle would darken. Often another animal observing this behavior would quickly swim away.” Keeping aside these unusual behaviors, what piqued scientists’ curiosity was the question “Why?” Why were these octopuses hanging around in these underwater cities? The answer, most likely, was food, the study author David Scheel shared with BBC Earth. “We suspect that this is an area where there’s a lot of food, relatively scarce shelter and plenty of predators," said Scheel.

"If you put that story together it seems that shelter is the most important thing. It looks fairly costly but probably better than going it without a den because predators is cruising by fairly commonly,” Scheel added. The discovery of these cephalopod cities is remarkable because it prompts scientists to think about other such worlds that the mysterious marine creatures might have engineered with their intelligence. Whatever the reason, socialization, aggression, or mating, these aquatic architects stimulate the marvel of scientists and mystics alike, for centuries. “That’s the beauty of the sea. It’s that unknown. There are still so many questions to be answered,” reflected Matt Slater, Marine Awareness Officer of the Cornwall Wildlife Trust, who has worked with giant Pacific octopuses.